Distribution and growth rates of immature hawksbill turtles Eretmochelys imbricata in Fernando de Noronha, Brazil

Abstract

Knowledge of life history parameters is essential for the effective management of species of conservation concern. For migratory marine vertebrates such as hawksbill sea turtles Eretmochelys imbricata, feeding aggregations are important developmental habitats, allowing the study of population dynamics. Here, we used data from a 31 yr mark-recapture study of juvenile hawksbill sea turtles in the Fernando de Noronha Archipelago, Brazil, to estimate key demographic parameters. Turtles recruit to the neritic habitat at similar sizes to those of other Atlantic hawksbill aggregations. The curved carapace length (CCL) at the first capture ranged from 28 to 84 cm (mean ± SD: 44.6 ± 9.8 cm). Median minimum residence time of turtles captured at least twice was 3.2 yr, whilst long-term minimum residence of up to 14 yr was also observed, with turtles showing site fidelity within the archipelago. The mean size of turtles captured was constant throughout time. Turtles grew on average 3.4 ± 2.2 cm yr-1 , with a monotonic expected growth rate function generally decreasing with increasing size. At these rates, hawksbill turtles in Fernando de Noronha would need to spend ca. 14−18 yr to reach minimum adult breeding size (~74 cm CCL). This mark-recapture study has been essential to understanding the ecology and demographic parameters of this regional hawksbill turtle neritic foraging ground.

Growth rate and projected age at sexual maturity for immature hawksbill turtles and green turtles foraging in the remote marine protected area of Aldabra Atoll

“…ID was used as a random, independent variable, as done when assessing growth rate over time (above). The equation was: gam(GR ~ s(CCL) + s(year) + s(RI), random = list(id ~ 1), method = "REML", family = Gaussian; see also Casale et al 2009;Colman et al 2015;Bellini et al 2019). GAMMs were run separately for the two species.…”

“…Since it is unknown how old turtles were before recruiting to Aldabra as a foraging ground, we estimated the age of turtles, since recruitment, with year 0 associated with the smallest median size for each species in the data. The integration equation, y(CCL i ) = y(CCL i−1 ) + (CCL i -CCL i−1 )/ r(CCL i ), was used, where: y(CCL i ) represents the age at the initial mean size, y(CCL i−1 ) is the age of the previous recorded mean size, and r(CCL i ) is the individual annual growth rate (Colman et al 2015;Bellini et al 2019). The integration was also performed to obtain con dence intervals from the GAMMs.…”

“…Variation between individual turtles and sites contributes to growth rates (e.g., Chaloupka et al 2004;Bjorndal, Parsons et al 2013), emphasizing the importance of collating demographics from various sites and regions. Additionally, population growth rates can be in uenced by human modi ed environments such as power plants (Eguchi et al 2012), though there is a lack of comparative life history parameters from sites with limited direct human impacts (Bellini et al 2019). The South-West Indian Ocean (Wallace et al 2010) Regional Management Units (RMU) host internationally important populations for both hawksbill turtles (Eretmochelys imbricata; Mortimer and Donnelly 2008) and green turtles (Chelonia mydas; Seminoff et al 2015).…”

Citizen science to determine sea turtles’ spatio-temporal parameters on a subtropical foraging ground

“…2 days, max. 14 years) during a long-term study (31 years) (Bellini et al 2019). Patterns of delity can be explained by habitat quality, which include optimal temperature, but also availability of food items (Metz et…”

“…Other di culties are related to tag loss, transmitter failure, and high value-added to certain equipment (Hebblewhite and Haydon 2010;Casale et al 2017). Nonetheless, mark-recapture still the most applied method because individuals are followed over time; thus, it is possible to obtain information on demographic parameters and population trends (see Bellini et al (2019)).…”